Delay action electric fuse



July 21, w36. c. E. sossoN ET AL 2,048,038

DELAY ACTION ELECTRIC FUSE I Filed Ja'n. 3o, 1954l Fl'cjl l N V EN TORS 0f! Char/e5 f. SOSS Horace ar/Ou/ A TTORNE Y.

Patented July 21, 1936 UNITED STATES PATENT OFFICE DELAY ACTION nuzc'rmcA FUSE Charles Edwin Sosson, Saltcoati and Horace Barlow, Falkirk, Scotland, assignors to imperial Chemical Industries Limited, a corporation of Great Britain Application January 30, 1934, Serial No. 709,040 In Great Britain February 7, 1933 This invention relates to delay action electric fuses, and more particularly to such a fuse having provisions for cooling the hot gases which escape when the fuse is red.

In delay action electric blasting fuses it is important to ensure the eiiicient filtration and cool'- ing of the hot escaping gases so that premature jor silica sand, or the lik'e, inside the case of the 2o delay fuse, or the provision of a metal sleeve around the outside of the Rise.

With the normal very small amount of -free space inside the tube, however, eiiicient filtration and. cooling are incompatible with good timing owing to the choking up of the lters by the carbonaceous dbris given oli from the burning igni tion and delay elements and carried along by the escaping gases. We have now found that this diiliculty may be overcome by the provision of a large space or deposition chamber within the delay action case, wherein this dbris is deposited,v in conjunction with a cooling sleeve surrounding the ignition end of the fuse.

. Our invention consists in a delay action electric blasting :fuse which comprisesan inner metal tube tting closely over the delay fuse element at one end, an electric igniter therefor, the leads of which pass through the seal at the other end ofthe tube, an outer tube surrounding the inner,

tube and joined toit at the end remote from the delay element and open at the end near vthe delay element, a ventV towards the end remote from which protrude's into the detonator or the like,

the initiation of which is to be delayed.

We prefer to form the-milled\rib or ribs if more than one be used as protuberance .on the inner @Q metal tube, and toform the junction between the lws being of substanti inner tube and the outer tube by pushing the outer tube over a plain protuberance on the inner tube situated at the end remote from the delay element and over the milled protuberance o r pro- Any leakage of gas at this end may ,'5'

tuberances. be additionally safeguarded against by pitching. vIt will be understood that the number of millings on the rib or rib can vary considerably, and by way of illustration e mention that a rib having 36 millings to th ch, the ridges and hol-*1o .the same width, is particularly suitable. If more than one rib is employed it is convenient to mill the rib vnearest;

the vent from the inner tube more coarsely than the succeeding rib or ribs. 15

The preferred form of the invention is illustratedin the accompanying drawing which. how- -ever, omits the detonator in the drawing. Fig. 1

is a central longitudinal section of the ignition end of a delay action blasting fuse showing a 20 portion only ofthe delay element. Fig. 2 is a cross section on the line 2 of Fig. 1. y

Referring to Fig. 1, the delay action electric "fuse comprises an inner metal tube,| fitted at one end with a delay element 2 and at the'other 25 .end with a plug 3 which may conveniently bei) made of rubber. Insulated leading wires l pass through the plug 3 to van igniter element 5, the various component parts being so arranged that for fuse of ordinary diameter, the distance be- 30 tween the delay element 2 and the plug is at least'20. mm. The space so formed is empty. 6X- cept for the igniter elementvand the leading wires thereto, and is much larger than the space normally provided in delayaction electric fuses. At 35 short distances from the plug end of the inner tube are provided two annular ribs 6 and 1 of which the rib 6 has a milled edge. Between the two ribs there is provided a vent hole 8 in the tube for the escapeof the gases. 40

Over the inner tube I is slipped an outer metal tube 9 which is made to t tightly over-the ribs,

r forming a seal with the unmilled rib and leaving an open annular space around the inner tube.

The outer tube 'nagconveniently be made abo/ut/ 45 1 greater in diameterthan the inner tui/ier". After assembly the-top of the delay fuse is /coated with pitch I0 down to the top junction tween the outer tube 9 andfthe'to'p rib 1, which assists in making the seal gas tight. 5 0

' The vent hole or holes 8 may be closed temporarily by any of the usual ineansof making such a vent waterproof, as for example,v by. means \of a strip of thin papershellacked on to the tube and coated with a waterprooiing dope, such as benzyl cellulose or nitrocellulose or material possessing similar properties.

On firing the' fuse, the emptyspace inside the' caping gases burst the seal over the ven't and Y escape along the outer sleeve by way of the milled rib or ribs.

The milled ribs act. as a-ltering device and along with the outer sleeve effectively cool the escaping gases. Y

Delay ac tion electric fuses made in accordance with our invention are of goodV shape from the point of view of keeping them water-tight, there being little tendency for water to find its way into the inner tube. No difficulty is experienced in obtaining consistent delay times. Provided their overall length is not too great they can be completely embedded in the blasting charges Withou fear of premature ignition thereof. y v

As it is advantageous that the delay action electric fuse should.be totally embedded in the cartridge, we prefer to arrange that the overall length, including the detonator, should be kept short. If very short cartridges are to be used,

however, it will not be possible for the delay action electric fuse tobe totally embedded within them.

now particularly described and ascerined the nature of our invention, and in what manner the same is to be performed, we declare that what we claim isz- 1. An improved delay action electric blasting fusecomprising an inner'metal tube tting closely over a delay fuse element at one end, an electric igniter therefor, the leads of which pass through the seal at .the other end of the tube, an outer tube 5 than is the said vent, the length of the inner tube being suiicient to provide a relatively large space for the deposition o'f the solid products of l5 combustion.

2. An improved delay actionV electric fuse as claimed in claim 1 wherein the distance between the delay element of the seal is not less than 20 mm. y

3. The delay action electric fuse of claim 1 in which the outer and the inner tube are attached by pushing the outer tube over a milled rib or ribs and an unmilled rib or ribs formed on the inner tube nearer its extremity than is the vent, 25 the junction at the outer unmilled rib being ren- 1 dered gas tight by means of a waterproong composition.

4. Thedelay action electric fuse of claim 1 wherein the vent between the inner and outer 30 K tubes is temporarily closed.

CHARLES EDWIN SOISSON'. HQRACE BARLOW. 

